The precisely relocated hypocenter of small earthquakes shows linear or zonal distribution,which can be used to determine the quantitative geometries of seismogenic fault by fitting a spatial plane through mathematical method and then to reveal the relationship between the earthquake spatial distribution and active tectonics.Using the seismicgenic fault fitting method,the geometries structure and motion mode of the seismogennic fault of the 1976 Tangshan M7.8 earthquake,the 1668 Tancheng M8 1/2 earthquake and the 2013 Lushan M7.0 blind earthquake is determined,the parameters is relatively consist with researches of deep structure detections which shows that the seismicgenic fault fitting method has important significance to active fault detection.

1303年在山西洪洞附近发生的8级巨大地震,是中国根据现存较为详细的文献记载史料所确定的最早的一次8级地震.这次地震距今已有700多年的历史,而地震所在区域至今仍有持续不断的小地震活动.本文根据地震破裂区1981年至2013年的中小地震精定位地震目录,采用震源断层面拟合方法,反演得到了1303年山西洪洞地震的震源断层面参数:走向19.3°、倾角88.5°、滑动角-170.0°.断层面长75.5 km,宽26.2 km,深度为地下11.12～37.35km.将地震破裂区的地震精确定位资料以近东西向的洪洞断裂为界划分为地震北段和地震南段,分段进行地震震源断层拟合,反演得到洪洞地震北段震源断层面参数:走向13.7°、倾角76.6°、滑动角-157.6°.断层面长32.7 km,宽21.7 km,深度为地下11.97～32.86 km;南段震源断层面参数:走向20.3°、倾角87.1°、滑动角-154.6°.断层面长45.9 km,宽16.6 km,深度为地下9.32 km～25.50 km.无论是分段还是不分段,反演得到的洪洞地震震源断层均是右倾的近直立断层,属于右旋走向滑动性质.分段计算得到的地震北段震源断层深度比南段更深,将反演得到的震源断层与临汾盆地深部构造最新研究成果进行了分析对比,北段震源断层深度及倾角大小与深地震剖面推测得到的深大断裂几乎相同.震源断层在地表的投影与洪洞地震的高烈度区能够较好地对应.

根据2008年9月至2013年10月金沙江下游水库地震台网监测资料,分析了蓄水期间水库地震影响区的地震活动和震源机制.向家坝水库蓄水1年多,蓄水后库首区A、B段的地震活动频次和强度都维持在较低水平.蓄水期间地震活动显著增加,集中分布在库区C段,并不是蓄水初期地震活动就增加,与库区2013年6月启动第二阶段蓄水有一定相关性,强度在3级地震活动水平.增加的地震活动位于近南北走向的翼子坝、玛瑙断裂的中段.这些局部地段蓄水后发生的地震,其震源的力学机制多为倾滑或正断型,分析认为部分地震为水库诱发岩溶或塌陷型地震,多数仍属构造地震.本文结果为水库诱发地震的研究提供了资料和震例.

Xiangjiaba Reservoir is currently Chinau0027s third largest reservoir and began impounding water at the end of 2012. After the impoundment,the water level rose to 71 m,while seismic activity near the dam was not significantly increased. At the end of June 2013,the reservoir began impounding water again,the water level continued to rise and flooded the tail region of the reservoir. In the reservoir area and the Xiluodu reservoir area in the upstream,a reservoir seismic network including 35 seismic stations was set up which can roundly record earthquakes in this area. According to the records of the reservoir seismic network from September 2007 to June 2013,only 38 earthquakes with ML≥1. 0occurred,0. 66 times a month on average,while in July- September 2013,186 earthquakes with ML≥1. 0 occurred,with an average of 62 events a month,nearly 100 times of that in the past. So,most of the earthquakes are induced earthquakes. At the same time 553 earthquakes with ML≤1. 0were also recorded in this area. A large number of small earthquakes occurring in the strong earthquake background area have caused a big stir. The source location of these earthquakes are rechecked based on 3D velocity model,94% of the rechecked focal depth is less than 5km. Based on observations of the reservoir seismic network and vertical P- and S-waveu0027s maximum amplitude ratio method,we inversed 9 focal mechanisms before the impoundment and 69 focal mechanisms after the impoundment in the tail region of the reservoir. Using these focal mechanisms,the stress field of the northern part and southern part of the study area is calculated in order to analyze the characteristic and cause of the induced earthquakes. The results indicate that most of the 69 focal mechanisms are strike-slip type,there is more transitional type,and less normal type and thrust type. The focal mechanisms spatial orientation is complex,fracture types are diverse,which may indicate that the stress state is uneven and the control of regional stress field to small earthquakes is weak. The stress field in the south and north is quite different and not consistent with regional stress field. The north shows compressive stress state while the south shows a state of weak extension. The Yaziba Fault,which passes through the tail region of reservoir,is an active fault,but does not control the induced seismicity,which may indicate that the reservoir storage inhibits the reverse fault activity. Carbonate rocks,limestone and karst cave are developed in the tail region. Analysis believes that reservoir water flows into the caves,penetrates into cracks and joints,leading to increased pore pressure,reducing the frictional strength and fracture strength and increasing reservoir water load which cause elastic deformation,so,it is believed that the combined action of all the above factors is the cause for the induced earthquakes.

近年来,我国大陆西部地区破坏性地震频发.通过地震现场的烈度考察和灾害调查等工作,迅速向社会公开发布地震烈度图,为地震应急救援、灾后恢复重建发挥重要作用.该文通过剖析2013年4月20日芦山7.0级地震烈度,发现其主要依据是居民点建筑物的破坏情况,和以滑坡为主的其他次生山地灾害、峰值加速度等代表的强地面运动分布存在显著差异,而受发震构造、震源分布、破裂过程、震源机制等因素约束不强.另外的几次地震也存在类似问题,并且有的地震修订烈度图可能不利于使用,所有地震都没有烈度异常区(点),越来越近似于共焦点等间距椭圆,烈度图的科学性存在疑问.针对这些问题,进一步提出对烈度速报问题的认识和展望.

The location parameters of the Zayu, Tibet M8. 6 earthquake sequence in 1950 in the published catalogues are poor, which cannot help further study of this great event. In order to provide more precise location results and some features of their spatial-temporal distributions, and to reveal the stress field in the corresponding region, we attempted to relocate this earthquake sequence and to determine the focal mechanisms. The data of global seismic stations from International Seismological Summary (ISS) and the Catalogue of China Earthquakes (BC 1831-AD 1969) were collected. The 16 events with M >= 6 of the Zayu, Tibet M8. 6 sequence were relocated by P arrivals at 239 worldwide stations using the routine location method and model of Chinese National Seismographic Network: Improved Geiger and the JB time tables. The corresponding fault plane solutions and composite fault plane solutions were determined by first motions of P waves based on the new relocations. (1) The relocations of 16 strong earthquakes of the Zayu M8. 6 sequence have been completed. It is shown that the epicenters in different periods appeared in different sub-regions: A foreshock which occurred on 23 Feb 1950 appeared in the 1st sub-region, the top of the great bend of the Yarlung Zangbo River, which lies at the north of Motuo. The mainshock and the following 7 aftershocks in 3 days which occurred from 15 Aug 1950 to 18 Aug 1950 were located in the 2st sub-region near Zayu and distributed along the north-west belt. The 3 aftershocks in period 3 which occurred from 22 Aug 1950 to 13 Sep 1950, were located in the 3st sub-region extending to the south, India and Myanmar. The 3 aftershocks in period 4 which occurred from 30 Sep 1950 to 15 Apr 1951 appeared in the 4st sub-region at Motuo and Cuona, west of the aftershock epicenter area. Another aftershock occurred on the 110th day after the mainshock, the epicenter of which returned to the place near the mainshock. (2) The focal mechanism solutions determined based on the relocations indicate that the NWW strike of a nodal plane of the mainshock is consistent with the NWW direction of the major axis of the aftershock epicenter area in the 2st sub-region. All compressive axes P and tensional axes T of the earthquake sequence are nearly horizontal, of which most dip angles are less than 20 degrees. The compressive axes of the mainshock and the aftershocks in the 2st sub-region are nearly north-south direction, and tension axes are nearly east-west direction. But in the 3st and 4st sub-region, the compressive axes of aftershocks are-nearly east-west direction, and tensional axes are nearly north-south direction. The 16 events of the Zayu, Tibet M8. 6 earthquake sequence in 1950 have been relocated. The new results are quite different from the parameters in the previous catalogues of which the locations of many aftershocks were exactly the same as the mainshock, i. e. only one point. The relocations indicate that the epicenters in different periods appeared in 4 different sub-regions rather than distributing along the determined rupture. The obvious correlation of these 4 sub-regions is clockwise rotation movement. The focal mechanism solutions determined based on the relocations display that the differences of focal mechanisms among the aftershocks of the sequence are large.

地震波在地球表面的反射波PP、SS由于需经地球表面的一次反射,因此属于远震记录观测到的震相.本文利用井下摆观测数据,对2003年吉林松原震群和2005年黑龙江林甸地震震相进行认真研究,根据台站附近的测井资料确定的上地壳速度模型,对选定的地表反射点进行地震波的走时计算,初步判定在特定的震中距内井下摆可以记录到地方震的地球表面反射波.为和远震记录的PP和SS震相相区别,本文暂定此震相为PgPg,SgSg.

1950年8月15日西藏察隅发生M8.6巨大地震.我们利用收集到的全球239个台站的P波资料,利用我国国家测震台网的常规定位方法和模型,对察隅M8.6强震序列进行了重新定位,并在此基础上重新计算了震源机制解.重定位后的结果表明,察隅M8.6强震序列显示出不同时段的震中分区分布特征:第1阶段是前震,1950年2月23日在墨脱北部雅鲁藏布江大拐弯的顶部发生;第2阶段是1950年8月15日-1950年8月18日,发生主震和之后3天内的余震,都分布在察隅附近,并且这些震中呈北西条带分布;第3阶段的余震是1950年8月22日—1950年9月13日,它们扩展到南部的印度和缅甸地区;第4阶段的余震是1950年9月30日-1951年4月15日,发生在西部的墨脱、错那等地.这四个分区的关联特点为顺时针旋移.重新计算后的震源机制解显示出:主震的NWW走向的节面与主震后2区内余震震中的NWW分布方向一致;序列中所有的压应力轴P和张应力轴T,都接近于水平向,其倾伏角大都小于20°;察隅主震和2区内余震的压应力轴P为近南北向,张应力轴T为近东西向;但3区和4区余震的P轴为近东西向,T轴为近南北向.反映出该强震序列中余震震源机制解的差异比较大.

2013年4月22日内蒙古通辽市科尔沁左翼后旗、辽宁阜新市彰武县交界发生5.3级地震.研究发现,该地震序列震中分布、震源机制及烈度考察极震区长轴方向均为近东西方向,与横贯震区的养畜牧河断裂走向一致,综合判定该断裂是5.3级地震的发震构造.

A big earthquake with M7 .7 was occurred in the southeast of Lang county in Tibet on July 29,1947.We collect the global observational phase readings of this event,and we re-determined the source parameters with the daily location method and technical of the Chinese national network and the ISC locator respectively.Both the relocated epicenters are at the near of Lilong rupture,we prefer the location results of the Chinese national network after our comparison and analysis,and we recalculated the focal mechanism based on this new results.It is consistent with the strike of Lilong rupture,the revised location is also at the Lilong rupture,this indicate that the Lilong rupture was probably the seismogenic fault.

芦山地震之后,岩崩灾害造成交通断绝,通往极重灾区乡镇的道路只有一条窄路;而极灾区仅仅限于5个乡镇,坍塌的楼房等大型废墟不多,大量投入的大型器械和运输车阻碍交通,成为救灾的瓶颈.在情况不明的条件下,军政领导应急过度在所难免.不能忽视,地震初期地震系统提供的信息存在不确定性:2 min地震基本参数速报的震级偏低很多;震区构造研究程度低,对主震的发震构造有不同认识,经现场考察之后提出发生在盲断裂的判断;快速提供的烈度图为对称的椭圆,没有考虑逆冲地震的上盘效应;矩张量解和破裂过程过于专业,也没有指出对于灾情分布的影响.上述问题表明,如何发挥地震科学技术的支撑引领作用,提高其在应急工作中的贡献率,是专业人员必须大力解决的问题.

Based on the seismic waveforms recorded by Hainan seismic network in the northern Hainan island since 2000, 103 earthquakes were relocated by double-difference method and some focal mechanisms were determined by amplitude ratio. We inverted the regional stress field from the focal mechanism and two focal fault planes from the precise hypocenters, and inferred the slip type of the focal fault under the regional stress field. Contrasting with the isoseismal line of the historical earthquake, the WNW focal fault located in the eastern central part of the meizoseismal area, which has the same direction as the major axis of the meizoseismal area. This indicates the focal fault may be the seismogenic structure of Qiongshan earthquake in 1605. The northeast wall of the high angle focal fault slipped down to southeast, which makes the NNW quadrant extensional and leads to the land subsidence into the sea. Another NS focal fault just located on the boundary between the Quaternaryvolcanic rocks and Quaternary basin where the lifting movement is the most intense. The eastern wall of the normal focal fault dropped, which was consistent with the sedimentary basin. The results show that this two focal faults are related to the historical earthquake and tectonic movement, but do not coincide with the surface fault, indicating an uncoordinated phenomenon between the shallow and deep tectonics.

1668年在山东郯城附近发生的81/2级巨大地震,是有史料记载以来发生在中国东部的最大地震.该地震发生在郯庐断裂带山东区段,震源区现代小震依然频繁.本文以震源区附近重新定位的百余个现今中小地震基本参数,反演得到1668年郯城81/2级大震震源断层产状:震源断层走向21.6°,倾角为89.5°,滑动角为148.9°,震源断层长度约180km,下界深度约为32 km,上界埋深约为4km左右,为北北东走向直立的右旋近走滑断层.震源断层在地壳浅表对应沂沭断裂带东地堑的安丘—莒县断裂(F5).根据81/2级大震地表地震断层和烈度分布研究成果对反演结果进行了分析,并结合震源区地震深度分布、地震波速度剖面等对81/2级地震的基本参数进行了讨论,认为各种结果之间能够相互验证,反演获得了理想结果.研究证明,对于震源区现代中小地震资料丰富的历史大地震,用该方法反演震源断层三维产状和错动性质是可行的.

We use the Centroid Moment Tensor (CMT) solution of the earthquakes occurred in Chile subduction to analyze the characteristics of focal mechanisms. We define the angle between P, B, and T axes of focal mechanisms and three stress axes of tectonic stress field as the consistency parameter, to research the dynamic changes of focal mechanism pattern in earthquake preparation area before the 2010 Maule, Chile earthquake. The result shows that the consistency parameter decreases before the earthquake, and the area of the lower consistent parameter visually coincides with the distribution of aftershocks. This phenomenon is similar to the Load-Unload Response Ratio (LURR) decreases prior to the occurrence of macro-fracture happened in the acoustic emission experiments involving large rock specimens under tri-axial stress.

1950年8月15日西藏发生8 6级巨大地震.经重新测定这次巨震序列的震源参数,推断出西藏察隅M8.6主震的震源断层,结合余震分布、极震区分布、震源机制、地震条带和活动断层相互验证了震源断层的科学合理性.

目前,测定地震震源机制解较多地通过P波初动、体波波形、面波波形和大地测量数据,然而针对中国测震台网建设之前发生的历史地震,利用以上方法测定震源机制解比较困难.

Shanxi tectonic belt is a historically earthquake-abundant area and the focal distribution of the majority of the strong earthquakes is controlled by the local north-south oriented structures on the tectonic belt. Using the cataclastic analysis method(CAM),we performed an inversion analysis on the stress state of focal mechanism solutions of earthquakes which happened on Shanxi tectonic belt from 1967 to 2010.Results show that spatial distributions of the maximum principal compressive stress axis of Shanxi tectonic belt have changed over time,with two different predominant directions,NW and NE,in different periods of time. When the maximum principal compressive stress axis is oriented in NE direction,the stress state is registered as horizontally shearing and horizontally extension on the north-south and southeast oriented local segments in turn. When the maximum principal compressive stress axis is oriented in NW direction,the stress state of north-south and northeast tectonic segments is primarily registered as horizontally shearing.

地震定位确定的震源位置表示的是地震初始破裂点的位置,震级低则震源体积也小,作为一级近似,可用初始破裂点表示中小地震的震源体的位置.虽然大量小震震源体未必相互衔接,但是它们共存于一个条带,应当具有成因上的联系.

Based on P and S wave travel times of local,regional and far earthquakes recorded on 115 station distributed in capital area and Handan network in Hebei Province,P and S wave velocity structures beneath Taihangshan tectonic belt and areas at its east were obtained in the depth of 300km by seismic tomography technology.The results show that,there exists obviously transversal unhomogeneous in upper mantle velocity profiles along Taihangshan tectonic belt,where its southern,middle and northern segments exhibits their different structure features.Beneath the area at the east of Taihangshan,the lithosphere is thin,and the asthenosphere here is at the depth of about 80km.But under the depth of 180km,the P wave velocity structures show large differences in S wave velocity structures,in which at the east area of North China there presents mainly high P wave velocity,while S wave velocity maintains relatively low in most areas of North China basins although the low velocity media is cut by high velocity bodies.The deep structures demonstrate that,the middle segment of Taihangshan had been affected strongly by the lithospheric thinning in North China,and its velocity structure is much consistent with that beneath the basins.While the tectonic activity in southern segment was controlled apparently by shallow faults,but the upper mantle may maintain the character of old orogen with thick lithosphere and more high velocity media in upper mantle.The northern segment of Taihang belt,located at the boundary of multi-tectonic area,is complicated in velocity structure,and part low velocity region may be connected with mantle upwelling.

<正>地震活动资料表明:苏州市及周围邻近地区,历史上没有发生过5级以上地震,现代仅仅有中小震活动。已经布设有江苏省、苏州市、浙江省、上海市数字地震台网,比较而言苏州附近是全国地震台网密度